The present invention relates to an active constant power supply apparatus. More particularly, the present invention relates to an active constant power supply apparatus which can rectify power having various intensities and frequencies without using a high capacity condenser for a smoothing circuit which degrades the power factor of a circuit, and can supply constant power to a load.
The precise control for power supply is very important in various fields. In particular, since current of an LED (light emitting diode) is significantly varied even if voltage is slightly changed, the precise current control is required.
According to the related art, as shown in FIG. 1, AC power supplied from an AC power supplier 10 is converted into DC voltage by a rectifier 11 and a smoothing circuit Cd, and constant voltage is supplied to a load by a pulse width controller 20.
In addition, under the designed input voltage of the AC power supplier 10, the turn-on of a switch Q is performed by driving the switch Q using a switch driver 23 when an oscillator 21 sets an RS-flip-flop 22 and the turn-off of the switch Q is performed by resetting the RS-flip-flop 22 using a switch turn-off decider 24 when voltage applied to a current detection resistor R is higher than reference voltage ZD due to over-current supplied to the switch turn-off decider 24 through a leading edge blanker 25.
Further, the current flowing through the switch Q is consecutively increased from a turn-on point of the switch Q due to a coil L serving as a charged device. In addition, under the designed input current of the AC power supplier 10, if the switch Q is turned on, the current detection resistance R is set such that the switch Q can be turned off by the switch turn-off decider 24. If the switch turn-off decider 24 is not operated, the switch Q is turned off at the point corresponding to 80% to 90% of the oscillation period of the oscillator 21.
However, according to the related art, when the constant power is supplied to the load 12 by SMPS (Switching Mode Power Supply) scheme, a high voltage/capacitance condenser for the smoothing circuit Cd is required to stably supply power to the load 12 by smoothing the AC power.
Therefore, the power factor is lowered to the level of 0.4 to 0.5 due to the condenser. In order to improve the power factor to the level of 0.9, an additional circuit for improving the power factor must be provided.
In addition, the high voltage/capacitance condenser for the smoothing circuit Cd is very expensive and increases the size of the circuit so that the physical size of the constant power supply module may be enlarged.